Tire pressure maintenance device

ABSTRACT

A device for maintaining a desired inflation pressure within a tire mounted on a wheel of a vehicle which includes a microcompressor having a flexible compression chamber and a magnetic element not on the wheel. As the compressor passes the magnet each wheel revolution, a small amount of atmospheric air is pumped into the tire, if needed. The magnet and the compressor need no other contact with the vehicle or the wheel and require no energy source on the wheel. An alternative embodiment uses an electrical coil on the wheel to pass the magnet inducing a voltage that drives a compressor on the wheel. As the coil passes the electromagnet it provides a split transformer that transfers electrical power to the wheel and permits two-way pulse data communication between the wheel and the vehicle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and is a continuation-in-part ofU.S. application Ser. No. 11/273,116 filed Nov. 14, 2005 entitled “TirePressure Maintenance Device,” the contents of which are whollyincorporated by reference herein and which claims priority toprovisional application Ser. No. 60/627,256 filed on Nov. 12, 2004.

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not Applicable

BACKGROUND

The present invention relates generally to vehicle tire pressuremaintenance, and more specifically, to a tire pressure maintenancedevice contained on a wheel of a vehicle that automatically regulatesand maintains a desired tire inflation pressure or amount of air in atire.

Under-inflation of vehicle tires is dangerous, deadly and common.Under-inflation is involved in hundreds of thousands of accidents, tensof thousands of injuries and hundreds of fatalities annually in theUnited States. During 2000, a large number of SUV rollovers and deathswere attributed to significantly under-inflated tires, bringingsignificant attention to the problem. With the hope of reducing theunacceptably high rate of accidents, injuries, and deaths related tounder-inflation, the United States Congress passed the TREAD Act of 2000that requires a warning system in new motor vehicles to indicate to theoperator when a tire is significantly underinflated. Consequently, theNational Highway Traffic Safety Administration (NHTSA) proposed a safetystandard requiring that, as of 2007, all new passenger cars, trucks,multipurpose passenger vehicles, or busses under 10,000 pounds must beequipped with a tire pressure monitoring system (TPMS) to warn a driverwhen any tire is under-inflated by 25% or more. The program is estimatedto cost well over one billion dollars annually.

However, even if the controversial TPMS program achieves its estimatesit will reduce under-inflation related accidents by only about twentypercent. Many industry experts doubt that it will help at all. Incontrast, a device that automatically maintains proper tire inflationwill eliminate almost all accidents, injuries, and deaths due tounder-inflation. In addition, an effective tire pressure maintenancedevice will improve fuel efficiency by about two percent and will reducetire tread wear by about ten percent. Such benefits will more than payfor the devices and save billions of dollars annually in the UnitedStates if implemented into widespread use.

The temperature of air in a tire has a major effect on the pressure ofair in the tire. This factor must be considered in any approach to tirepressure maintenance. FIG. 1 shows how tire pressure varies withtemperature according to the ideal gas law. The fourpressure-temperature (P-T) lines illustrate the pressure-temperaturebehavior of a tire filled to 32 psi at air temperatures of 20, 40, 60,and 80° F., assuming a constant tire volume. The four P-T linesrepresent four different amounts of air in the tire. Ambient temperaturevariations and tire heating from rolling make tire temperatures andpressures move up and down along the P-T line denoting the amount of airin the tire. A tire will move to a higher P-T line only when air isadded and to a lower line only when air is released or leaks out of thetire.

As shown in FIG. 1, the pressure in a tire increases and decreases about1 psi with temperature increases and decreases of 10° F. Normally, thetemperature in the tire increases about 2 to 5 psi above its coldpressure at ambient temperature due to the heat caused by flexing of theside walls and friction from road contact as the car is driven. Mostunder-inflation is due to inadequate manual tire pressure maintenance.The recommended manual tire inflation procedure is to fill each tiremonthly to the manufacturer's recommended cold pressure (MRCP) orplacard pressure at ambient temperature. In practice, tires are usuallyfilled less often and also while warm from driving. Further, an ambienttemperature drop of 50° F., which is possible within a day and commonwithin a month, reduces tire pressure by about 5 psi. Thus, tirepressures frequently fall 8 psi below the MRCP, typically abouttwenty-five percent, without considering the normal leak rate of about 1psi per month.

Two approaches to automatic tire pressure maintenance goals are:

-   -   1) Constant Pressure by maintaining the MRCP independent of        temperature by adding air when the warm tire pressure is below        its warm objective, which is about 3 psi above the MRCP; and    -   2) Constant Amount of Air by maintaining the amount of air in        the tire that produces the MRCP at a selected temperature by        adding air any time the tire temperature and pressure fall below        the related PT line.

Both approaches replace air that leaks from tires and assures lessvariation from the MRCP than manual inflation procedures, with orwithout a TPMS. Moreover, the constant amount of air approach willminimize deviations from the PT line due to temperature changes and willminimize the amount of air pumped into a tire to maintain the desiredinflation pressure.

Many patents have been granted on approaches to automatically maintainthe desired inflation pressure in pneumatic tires. None of theseapproaches address temperature variation significantly. One suchapproach involves a difficult generation of two continuous out of phaseAC voltages that are rectified to provide a continuous DC power sourcefor a DC motor-driven air compressor on the wheel. Another approachdiscloses a battery-operated compressor contained on a wheel with nopractical means for recharging the battery. Another approach requires aTPMS or an on-wheel pressure sensor to send low tire pressure data fromthe wheel to the vehicle body in order to activate an electromagnet thatdrives a compressor on the wheel. However, none of these approaches haveproduced a practical device. Therefore, there exists a need in the artfor a tire pressure maintenance means that:

-   automatically maintains proper tire inflation without operator    attention or maintenance;-   is small, simple, practical, inexpensive and provides long term    reliable operation;-   is self-contained on a wheel assembly and operated by wheel    rotation;-   is fail safe such that failure does not cause deflation or    over-inflation of a tire;-   alerts drivers to excessive tire leaks or failures; and-   provides a higher emergency inflation rate to mitigate leak rates    and increase the time for drivers to reach a safe place.

BRIEF SUMMARY

A new device automatically maintains a desired inflation pressure of aninterior of a tire mounted on a wheel of a vehicle and overcomes normalcar tire leakage. A magnetic element is attached to a stationary part ofa wheel assembly and a compressor, such as a microcompressor, is mountedon the rotating wheel. The compressor is magnetically activated as itpasses near the magnetic element. The magnetic element, which may be astationary permanent magnet or electromagnet, may thus be used as thedriving element, and several magnetically-driven compressorconfigurations are disclosed herein. The compressor may perform at leastone cycle per wheel revolution. Alternatively, an electrical coil can bemounted on the wheel to pass near the magnetic element, thereby inducingvoltage pulses in the coil to provide on-wheel electrical power to runan electrically-driven compressor that is mounted at another location onthe wheel.

Various embodiments of the device using a magnetic element include:

-   -   1) A stationary permanent magnet that drives an on-wheel        magnetically activated compressor.    -   2) A stationary electromagnet that drives an on-wheel        magnetically activated compressor.    -   3) A stationary permanent magnet and an on-wheel coil that drive        an on-wheel electrically activated compressor.    -   4) A stationary electromagnet and an on-wheel coil that form an        intermittent split transformer that transfers electrical power        to the wheel to drive an on-wheel electrically activated        compressor and exchanges pulse coded data between the wheel and        vehicle frame.

As mentioned above, the magnetic element is mounted on the stationarymember of the wheel assembly, such as a brake housing, at a radialdistance from the axis of rotation of the wheel assembly. The compressoror coil may be mounted on the wheel such that it passes near the magnetduring each revolution of the wheel. The magnetic element produces amagnetic field, which creates a magnetic force on the compressor.Additionally, a bias force, which opposes the magnetic force, may beproduced by a bias member or source within the compressor.Alternatively, the bias force may be produced centrifugally or byanother magnet or pole.

In one embodiment, the compressor comprises a flexible compressionchamber and a ferromagnetic actuator that is attached to one end of thechamber. The magnetic force and the bias force cause the ferromagneticactuator to move back and forth in response to the opposing forces whichcauses the volume of the compression chamber to sequentially expand andcontract. The flexible compression chamber may comprise a bellows havingtwo circular ends and collapsible side walls, where one end of thebellows is fixed in relation to the body of the compressor.Alternatively, the flexible compression chamber may further comprise aflexible diaphragm that bounds the flexible compression chamber on oneend. The flexible diaphragm may further comprise ferromagnetic particlesdispersed therein. The compressor may further comprise an output valvethat is in communication with an output port. The output port may be influid communication with an aperture in the rim. Alternatively, apneumatic tube may connect the output port to the tire's valve stem.When the pressure in the compression chamber exceeds the tire pressureand does not exceed the desired inflation pressure, the output valveopens and compressed air flows into the tire. Thus, the transit of themagnetic field by the compressor causes air to be added to the tire whenneeded to raise the tire pressure to the desired pressure with nophysical contact between the wheel and the vehicle frame for passingpower or data.

One of the simplest, smallest embodiments of the present invention usesa stationary permanent magnet and a magnetically activated compressor onthe wheel. A magnet in the compressor provides a continuous bias forcethat holds the flexible compression chamber closed, except when it isoverpowered by passing near the magnetic element off the wheel thatbriefly opens the flexible compression chamber, thus creating thereciprocating motion of the compressor. The force of the magneticelement on the actuator is stronger than that of the bias force. Thebias force limits the pressure produced to the desired inflationtemperature. The bias force may vary the desired inflation pressure withtemperature to match the ideal gas law, thereby regulating the amount ofair in the tire to produce the desired inflation pressure at a selectedtemperature. A compressor that will supply 0.001 to 0.002 cubic inch offree air to a tire each wheel revolution is capable of increasing anormal car tire pressure by 1 psi within 50 to 100 miles of driving,well above normal leakage rates. Such a magnetically-driven compressormay occupy a fraction of a cubic inch and weigh a fraction of an ounce.The device can be added to a Tire Pressure Maintenance System (TPMS)equipped vehicle, but a TPMS may add little value to a vehicle equippedwith a device that maintains the desired tire pressure.

An alternative embodiment uses a stationary electromagnet and a rotatingelectrical coil on the wheel to form an intermittent split pulsetransformer briefly during each revolution as the coil passes thestationary electromagnet. The intermittent transformer transferselectrical power from the vehicle to the wheel and provides two-waypulse communication between the vehicle and wheels. The electrical poweron the wheel activates an electrically-driven compressor to maintain thedesired tire inflation and provides power to on-wheel electronics. Anon-wheel electronic controller may manage compressor operation andcontrol two-way communication with a central controller on the vehicle.It may send data on compressor utilization or output flow rate to thecentral controller from which too high a rate suggests a leak, and toolow a rate suggests a device failure. The central controller warns thedriver of either such condition by a simple display. Addition of a smallrechargeable battery whose charge is maintained by power from thetransformer provides reserve power to run the compressor at high speedto mitigate rapid leaks, increasing time to reach safety before the tiregoes flat.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the various embodimentsdisclosed herein will be better understood with respect to the followingdescription and drawings, in which like numbers refer to like partsthroughout, and in which:

FIG. 1 is a graph showing the relationship of air pressure andtemperature along pressure-temperature lines in a tire filled with fourdifferent amounts of air to the manufacturer's recommended cold pressure(MRCP) at different temperatures;

FIG. 2 is a partial cross-section view of an exemplary automobile wheelassembly showing an example location of a magnetic element on astationary disc brake caliper housing and a magnetically-drivencompressor located on a wheel rim at a time when the wheel rotationplaces them adjacent in accordance with an embodiment of the presentinvention;

FIG. 3 is an oblique view illustrating the magnetic element andcompressor arrangement of FIG. 2 in greater detail;

FIG. 4A is a cross-section view of an intake position of a compressorthat includes a flexible compression chamber in the form of a bellows,with a magnetic actuator and bias magnets, depicted at a positionadjacent to the stationary permanent magnet;

FIG. 4B is a cross-sectional view of an output position of thecompressor shown in FIG. 4A;

FIG. 5 is a cross-sectional view of another embodiment of a compressorhaving a flexible compression chamber in which a compression springprovides the bias force;

FIG. 6A is a cross-sectional view in which the compression chamber isbounded on one side by a flexible diaphragm with embedded ferromagneticparticles that also serves as the actuator, shown in the input positionin the presence of a stationary permanent magnet;

FIG. 6B is a cross-sectional view of an output position of the magneticdiaphragm compressor shown in FIG. 6A;

FIG. 7 is a partial cross-section view of another example arrangement onan automobile wheel assembly with a stationary electromagnet and amagnetically-driven compressor wherein the compressor output isconnected to a tire valve stem by a pneumatic tube;

FIG. 8 is an oblique view of a magnetically-driven compressor that isactivated by passing each pole of an electromagnet;

FIG. 9 is a partial cross-section view of an exemplary automobile wheelassembly wherein the stationary permanent magnet is mounted on a drumbrake backing plate of the wheel assembly where an electrical coil,mounted on a wheel rim, passes close to the magnetic element and is inelectrical communication with an electrically-driven compressor locatedover a wheel hub and in fluid communication with the valve stem via thepneumatic tube;

FIG. 10 is a cross-section view of a partial automobile wheel assemblywith an electromagnet mounted on a disc brake caliper housing and anelectrical coil mounted on a wheel spoke thereby forming an intermittentsplit transformer for transferring electrical power from the vehicle tothe wheel and for communicating between the wheel and a centralcontroller on the vehicle;

FIG. 11 is a schematic diagram of the electromagnet and electrical coilforming an intermittent split pulse transformer that provides inducedelectrical pulses directly to the electrically-driven compressor;

FIG. 12 is a schematic diagram of an embodiment using the intermittentsplit pulse transformer to transfer electrical power from the vehicle tooperate the electrically-driven compressor and on-wheel electronics, andto transfer pulse coded data in both directions between the vehicleframe and the wheel to alert a driver to suspected leaks or failures;and

FIG. 13 is a schematic diagram of an embodiment as in FIG. 11 in whichthe magnetically-driven compressor and the electrical coil pass theelectromagnet sequentially, the electrical coil supplying electricalpower to only the on-wheel electronics and providing two-way pulse codedcommunication of alerts and control data between the vehicle and thewheel.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for purposes ofillustrating the various embodiments of the present invention and notfor purposes of limiting the same, FIG. 2 is a cross-section view of apartial automobile wheel assembly 10 and a device 12 for maintaining adesired inflation pressure of an interior of a tire 14 by using therotation of the wheel 22 with respect to the wheel assembly 10. As isknown in the art, various configurations exist for wheel assemblies 10.A wheel assembly 10 is generally movably attached to a vehicle frame bya suspension and in some cases, by a steering mechanism. For simplicity,the embodiments of the present invention will be discussed withreference to generic elements that are commonly present in most wheelassemblies 10. However, as will be understood, implementations of thepresent invention may be retrofitted into a variety of existing wheelassemblies 10 or designed into new wheel assemblies 10 of differingconfigurations.

Wheel assemblies 10 may include many members that do not rotate with thewheel 22, some of which, such as a brake assembly, retain a very closerelationship with the wheel. Such items are referred to hereafter asstationary members, meaning stationary with respect to a wheel assembly10. Although they may move with respect to the vehicle frame, they donot rotate with the wheel.

Examples of magnetic elements in association with a magnetically drivencompressor having a flexible compression chamber are shown in FIGS. 4,5, and 6 with examples of mounting configurations in FIGS. 2, 3, 7, 8and 9. These figures are generally schematic illustrations of conceptsrather than realistic design illustrations. For simplicity, filters andmeans to vary the desired inflation pressure with temperature are notshown in all cases, although they are contemplated. In most embodimentsthe compressor may be mounted to the wheel rim 28 as shown in FIGS. 2, 3and 8 or to a wheel spoke 96 as shown in FIGS. 7 and 9. Compressoroutput may be by a direct penetration of the rim 28 by attaching theoutput port 66 through a hole 64 in the rim as shown in FIGS. 2, 3 and 8or by pneumatic tube 70 to the wheel's valve stem 72 as shown in FIGS.7, 9 and 10. The magnetic element 30 may be attached to the brakehousing 18 as shown in FIG. 2 or any other stationary member of thewheel assembly 10 where the compressor 32 can be mounted to pass closeto it. The shapes and sizes of magnetic members may assume many variedconfigurations. Different biasing means may be utilized such ascentrifugal force, a magnet or a spring for the biasing force. Othersuch means are described in Applicant's co-pending application, U.S.patent Ser. No. 11/273,116 which was filed on Nov. 24, 2005, and ishereby incorporated by reference in its entirety for all purposes.

As shown in FIG. 2, the wheel assembly 10 may include a stationarymember such as a disc brake caliper housing 18 or a drum brake backingplate 20, as shown in FIG. 5, as well as any other of a variety ofstationary members of a wheel assembly 10. Further, FIGS. 2 and 3 alsoillustrate that the wheel assembly 10 includes a wheel 22 that definesan interior portion 24 and an axis of rotation 26. It is contemplatedthat the interior portion 24 of the wheel 22 may refer to numerouslocations along the wheel 22, such as a wheel rim 28 or a wheel spoke96. The tire inflation device 12 comprises at least one stationarymagnetic element 30 and a compressor 32 that rotates with the wheel 22.The magnetic element 30 can be mounted on a stationary member at aradial distance r from the axis of rotation 26. According to anembodiment of the present invention, such as the embodiment shown inFIG. 4, the magnetic element 30 is operative to produce a magnetic field36 that the magnetically-driven compressor 32 transits once per wheelrevolution. The magnetic element 30 may be a stationary permanent magnet37 or an electromagnet 38. The magnetic element 30 may further bepowered by receiving a current from a power source.

The compressor 32 is mounted on the interior portion 24 of the wheel 22.Thus, as the wheel 22 rotates relative to the stationary member of thewheel assembly 10, the compressor 32 transits the magnetic field 36during each revolution of the wheel 22. In response to the presence ofthe magnetic field 36, the compressor 32 operates to maintain thedesired inflation pressure within the tire 14 by intaking air from theatmosphere, compressing the air, and outputting the air into the tire14, when needed. Thus, the compressor 32 is in fluid communication withboth of the atmosphere and the tire 14. The compressor 32, which may bea magnetic compressor, further includes a compressor body 44. FIGS. 2and 3 further illustrate the relationship of the compressor 32 withrespect to the magnetic element 30 as the compressor 32 transits themagnetic field, as shown in FIG. 4A. The magnetic element 30 and thecompressor 32 are disposed at approximately the same radial distance rfrom the axis of rotation 26. The compressor 32 is positioned to passclose to the magnetic element 30 during each rotation of the wheel 22.It is contemplated that various modifications to the generalconfiguration may be implemented so as to further enhance the magneticcommunication of the magnetic element 30 and the compressor 32 and tofacilitate mounting on various wheel assemblies 10.

In addition to the features already mentioned, the device 12 furtherincludes means for regulating output pressure of the compressed air tothe desired inflation pressure. As will be noted further below, theregulation of the output pressure of the compressed air may beaccomplished without off-wheel aid. Thus, embodiments of the presentinvention may operate independent of controllers, regulators, or otherdevices and provide an independent, self-sufficient device thatmaintains the desired inflation pressure within the tire 14 without anyoutside source of power or data being attached to the wheel.

Referring now to FIGS. 4A, there is illustrated a cross-section view ofa magnetic element 30 and the compressor 32 as the compressor 32transits the magnetic field 36. In the embodiment shown in FIGS. 4A and4B, the compressor 32 includes a flexible compression chamber 33 and anactuator 35. The flexible compression chamber 33 is collapsible in thatit defines a chamber volume v, which chamber volume v may be increasedor decreased by the action of the actuator 35. The flexible compressionchamber 33 may be in the form of bellows, such as shown in FIGS. 4A and4B, or the flexible compression chamber 33 may comprise any similarstructure that defines a chamber volume that is collapsible in responseto the transit of the magnetic field 36 by the compressor 32. Thebellows may have two circular ends, each end may be in communicationwith the collapsible sidewalls, one end may contain an input valve andthe other end may contain an output valve, as further described herein,and collapsible sidewalls. The input valve and the output valve mayfurther be incorporated into the bellows. Preferably one end of theflexible compression chamber 33 is fixed in relation to one end of thebody of the compressor. As with any flexible material that is constantlyflexed, the flexible compression chamber 33 may be subject to fatigue.Thus, the flexible compression chamber 33 should be constructed from adurable material that is capable of withstanding factors including heatand constant motion.

The actuator 35 may be ferromagnetic such that it is responsive tomagnetic forces. Accordingly, at least one of the two opposing forces iscaused by the magnetic element 30, which may be a stationary permanentmagnet. The compressor 32 further requires no connected power source forits operation. Alternatively, the magnetic element 30 may be anelectromagnet that may be energized while the compressor is transitingits field. Generally, the ferromagnetic actuator 35 is attached to oneend of the flexible compression chamber 33 and moves back and forth withrespect to the opposite end of the flexible compression chamber 33 inresponse to alternating opposing forces. The actuator 35 is slidablypositionable with respect to the flexible compression chamber 33 toreciprocate between an input position, as shown in FIG. 4A and an outputposition, as shown in FIG. 4B. This action sequentially expands andcontracts the volume of the flexible compression chamber 33.

As the compressor 32 passes the magnetic element 30, it passes throughthe magnetic flux which follows the path of the magnetic field 36 asshown by the arrows. It should be noted that the magnetic field 36,which is well-known in the art as being a three-dimensional phenomenon,is represented by the two dimensional magnetic flux path shown in theFigures. The magnetic element 30 may be wider than the compressor 32 inthe direction of relative motion to lengthen the time that the fullmagnetic force is applied to the compressor 32 as it transits themagnetic field, as indicated in FIG. 3.

The compressor 32 may include an intake valve 46, an output valve 48, acentrifugal valve 78, an intake plenum 86, and an intake port 88. Theintake port 88 and the centrifugal valve 78 are operative to intake airinto the compressor 32. The compressor 32 utilizes the intake and outputvalves 46, 48 to maintain the desired inflation pressure of the tire 14.Specifically, the intake valve 46 is preferably a one-way check valvethat is operative to intake air into the compression chamber 33 duringthe intake or expansion stroke. The output valve 48 is preferably also aone-way check valve that is operative to output air from the compressionchamber 33 into the output port 66 during the output or compressionstroke. The output valve 48 is further in fluid communication with thetire 14. The intake and output valves 46, 48 are preferably check valvesto insure that no air from the tire 14 escapes to the atmosphere.Further, when the flexible compression chamber 33 is expelling air intothe tire 14, the intake check valve 46 may insure that no air intendedfor the tire 14 exits through the intake valve 46

Referring still to FIGS. 4A and 4B, the air path through the compressor32 begins at the centrifugal valve 78 at the intake port 88. A biasmagnet 60 holds the centrifugal valve 78 closed at vehicle speeds belowa predetermined speed, for example 15 miles per hour, at which thecentrifugal force expels potential liquid or solid contaminants from thearea of the intake port 88, preventing their entry through thecentrifugal valve 78. Above the predetermined speed, the centrifugalforce on the centrifugal valve 78 overcomes the magnetic bias forceholding the centrifugal valve 78 closed and opens the centrifugal valve78 to allow clean air to enter the intake plenum 86. The compressor body44 around the centrifugal valve 78 may be shaped to modify the air flowto deflect airborne particles away and reduce pressure differences dueto the Bernoulli Effect. The intake plenum 86 may occupy unused spacewithin the compressor body 44. An air filter and a membrane that resistsliquid passage may be placed in the intake plenum 86 in the path betweenthe centrifugal valve 78 and the intake valve 46.

As shown in FIG. 4B, two bias magnets 60 apply a bias force on theferromagnetic actuator 35 to hold it in the output position while thecompressor 32 is not in the magnetic field 36 of the magnetic element30, which minimizes the volume of the flexible compression chamber 33.An intake stroke of the actuator 35 may occur as the compressor 32transits the magnetic field 36 and the magnetic field 36 acts on theactuator 35 to draw one end of the flexible compression chamber 33 awayfrom its opposite and fixed end. Specifically, when the compressor 32rotates to the position adjacent the magnetic element 30, the magneticforce applied by the magnetic element 30 on the actuator 35 overpowersthe bias force and pulls the actuator 35 out on the intake stroke,maximizing the chamber volume of the flexible compression chamber 33, asshown in FIG. 4A. The outward movement of the actuator 35 increases thechamber volume of the flexible compression chamber 33 and creates apartial vacuum in the flexible compression chamber 33 that opens theintake valve 46 and draws air in from the intake plenum 86. As thecompressor 32 passes the magnetic element 30 the magnetic flux followsthe path of the magnetic field 36, as shown by the arrows in FIG. 4,through the air gaps, the ferromagnetic actuator 35 and the magneticelement 30. The intake position is achieved when the actuator 35 ispositioned such that the flexible compression chamber 33 hassubstantially a maximum chamber volume.

The actuator 35 is further operative to expel air from the flexiblecompression chamber 33 into the tire 14 by way of the output valve 48 asthe actuator 35 moves toward an output position during an output stroke,in which the actuator 35 is positioned with the flexible compressionchamber 33 substantially having a minimum chamber volume. Thus, as thecompressor 32 completes its transit of the magnetic element 30, the biasforce of the bias magnets 60 on the actuator 35 returns the actuator 35to an output position on an output stroke. The output stroke isperformed when the actuator 35 is pulled away from its open positionwhich reduces the chamber volume of the flexible compression chamber 33and causes the air within the flexible compression chamber 33 to becompressed increasing its pressure. If the maximum pressure provided bythe bias force is less than the tire pressure that appears in the outputport 66 the output valve 48 remains closed and no air is forced into thetire 14. If the pressure created in the flexible compression chamber 33by the bias force exceeds the tire pressure, the output valve 48 opensand air flows into the output port 66 and tire 14.

The compressed air may enter the tire 14 from the output port 66 throughfluid communication with an aperture 64 of the rim 28, as shown in FIGS.2 and 3. Alternatively a pneumatic tube 70 may connect the output port66 to a valve stem 72, as shown in FIG. 6, such that the output port 66maintains the same air pressure as the tire. As shown in FIGS. 4A and4B, the intake and output valves 46, 48 may provide two one-way checkvalves that prevent air from flowing backwards from the tire 14 throughthe compressor 32 in the event of a valve failure in the open position.The compressor 32 may further comprise an additional check valve that ispositioned between the output valve 48 and the valve stem 72 to preventair from leaking out of the tire. The magnetic element may be either anelectromagnet or a stationary permanent magnet.

Although it is preferred that the magnetic element 30 drive the inputstroke and the bias member 60 drive the output stroke, it iscontemplated that the magnetic element 30 may drive the output strokeand that the bias force may drive the input stroke of the actuator 35.

Two alternative approaches to tire safety may be followed utilizingembodiments of the present invention. First, one may seek to fix thedesired inflation pressure at the MRCP or other constant pressure asdesired. As such, the compressor 32 may be required to add air to thetire 14 to compensate for pressure losses due to leaks or drops in theambient temperature. As an alternative to the fixed constant pressureapproach, one may seek to maintain constant the amount of air in thetire 14. Specifically, one may seek to maintain constant the mass of airparticles in the tire 14. For example, the compressor 32 may vary thebias force with temperature to make the desired inflation pressureapproximate a selected P-T line 92 in FIG. 1. This is achieved bymaintaining a constant ratio of absolute pressure to absolutetemperature in the tire. This maintains the amount (mass) of air in thetire 14 constant at the amount of air that produces the MRCP at thechosen average ambient temperature several psi above the MRCP. Each P-Tline 92 in FIG. 1 represents the P-T relationship of a specific amountof air in the tire 14 according to the ideal gas law (PV=nRT), assumingconstant volume. For example, the compressor 32 may be configured tofollow the P-T line 92 that intersects the horizontal MRCP 32 psi lineat 60° F. That line becomes the desired P-T line 92 for the compressor32. To maintain the desired amount of air in the tire 14, the bias forceis increased with temperature to increase the desired inflation pressurewith temperature. The mounting of the bias magnet 60 may be configuredto vary its position with temperature thereby changing the bias forcewith temperature to approximate the selected P-T line. The compressor 32adds air to the tire 14 when the pressure-temperature (P-T point) of theair in the tire 14 is below the desired P-T line 92.

During installation of the device 12, the bias force of the compressor32 may be selected or adjusted to follow a desired P-T line 92(“compressor's PT line”) that intersects the MRCP at an average ambienttemperature for the area of use. The tire pressure normally stays on aP-T line determined by the amount of air in the tire. Of course,occasional additions by the compressor 32 to the amount of air in thetire 14 will be required due to leakage in the tire 14. In other words,the compressor 32 maintains the amount of air in the tire 14 constant,and the pressure in the tire 14 may fluctuate with temperature. ThisConstant Amount of Air approach may require adding less air to the tireand may keep the tire pressure closer to the desired pressure than thesimpler Constant Pressure approach. Thus, in the fixed-amount-of-airalternative, only when air is added or released (or escapes) will thetire move to a higher (or lower) P-T line. If the tire's P-T point isbelow the compressor's desired P-T line 92, the compressor 32 pumps asmall amount of air into the tire 14 each wheel 22 revolution. If thetire's P-T point is above the compressor's P-T line 92, no air is pumpedinto the tire 14 and normal leaks bring the tire's P-T point down to thecompressor's P-T line 92. Using this fixed-amount-of-air paradigm, thecompressor 32 replaces leakage air and maintains the amount of air inthe tire 14 nearly constant, keeping it on the selected compressor P-Tline 92 and minimizing the amount of air that must be added to the tire14.

The bias magnets 60 may be mounted at one end of temperature sensitivepositioning rods that establish the separation of the bias magnets 60from the actuator 35 for three purposes: (1) to select the compressor'sP-T line 92; (2) to vary the desired inflation pressure with temperatureto match the selected P-T line 92; and (3) to offset the bias magnets'decreasing strength with increasing temperature. The positioning rod hasa high thermal coefficient of expansion (TCE) and is mounted to providegood thermal communication with the air in the tire. By configuring theTCE materials, their exposure to the air in the tire, and the separationof the bias magnets from the actuator, the desired inflation pressureprovided by the bias force may be established.

FIG. 5 shows another embodiment of a flexible compressible chamber 33having a bellows configuration. The bellows are in the open positionsimilar to that shown in FIG. 4A in which the bias force is provided bya compression spring 62 attached to the actuator 35 and to thecompressor body 44 such that it applies a continuous force to close thecompression chamber. The transit of the magnetic field 36 of themagnetic element 30 applies an attractive magnetic force to the actuator35 that overcomes the bias force of the compression spring 62 and causesthe intake stroke, which expands the volume of the compression chamber33. When the compressor moves out of the magnetic field 36, the biasforce of the compression spring 62 pulls the actuator 35 back on thecompression stroke, which reduces the volume of the flexible compressionchamber 33. FIG. 5 further shows a different means of bonding anelastomeric bellows material to the actuator. As such, the device mayfurther include a flapper valve as part of the bellows to avoid sealingproblems. The compressor 32 further includes two bumpers 140, whichprotect the body of the compressor from the motion of the ferromagneticactuator 35.

In the constant pressure approach, the bias force is selected oradjusted to the desired tire pressure, slightly above the MRCP, at theaverage ambient temperature. Thus, selecting or adjusting the bias forceto the desired inflation pressure fixes the maximum pressure to beapplied to the tire 14 and is used to establish the desired tireinflation pressure. The bias force on the actuator 35 and the area bywhich the actuator 35 applies force to the flexible compression chamber33 determines the maximum pressure that the compressor 32 can produce.In this manner, the bias force is utilized to regulate pressure. Forexample, if the bias force on the actuator is 1.7 pounds and theactuator area is 0.05 square inches, the bias pressure is 34 psi, whichis the maximum pressure produced. The bias force may be adjusted byadjusting the spacing of each bias magnet 60 in FIG. 4B in relation tothe actuator 35 when the flexible compression chamber 33 is in an outputposition. Providing a calibrated adjustment to the bias force may permitmanual change of the desired tire pressure to adapt to seasons, loads orother conditions. If a tire is inadvertently filled with too much airthe normal tire leak rate will gradually correct this without compressoroperation. The compressor 32 may be sized to overcome a nominal tireleakage rate with a vehicle travel rate, such as miles per month.

FIGS. 6A and 6B show a magnetically-driven diaphragm compressor 32embodiment whose intake position is illustrated in FIG. 6A and outputposition is illustrated in FIG. 6B. The flexible compression chamber isbounded on one side by a flexible diaphragm 35 that is operative to:increase the volume of the chamber 33 and take in air through the intakevalve 46 and decrease the volume of the chamber expelling air throughthe output valve 48. The magnetic element 30 is shown as a permanentmagnet but could easily be an electromagnet. The flexible magneticactuator 58 preferably has ferromagnetic particles embedded in aflexible diaphragm material. A short pneumatic tube 70 attached to theoutput port 66 conveys the output air to the tire valve stem 72, asshown in FIG. 7. FIG. 6A shows the compressor 32 adjacent the magneticelement 30 where the flexible magnetic actuator 58 is magnetically drawnto the intake position by the magnetic element 30, drawing air into thecompression chamber 33 from the centrifugal intake valve 78, the intakeplenum 86, the filter 80, the membrane 79, and the intake check valve46. FIG. 6B shows the flexible magnetic actuator 58 held in the outputposition by the bias magnet 60 in the absence of the magnetic element30, forcing the compressed output air out of the compression chamber 33through the output check valve 48. The compressor body 44 is mostlynon-magnetic, but includes two ferromagnetic pole extenders 61 thateffectively shorten the air gap between the magnetic element 30 and theflexible magnetic actuator 58.

FIG. 7 shows an example mounting with an electromagnet 38 mounted on adrum brake backing plate 20 and the compressor 32 mounted on the wheelspoke 96 with a pneumatic tube 70 connecting the output port 66 of thecompressor 32 to the valve stem 72. A central controller 100 directscurrent from the vehicle battery 40 to an electromagnet winding 116, asshown in FIG. 8, to produce the magnetic field 36 only while thecompressor 32 transits the magnetic field 36. It may determine thelocation and speed of the compressor 32 on the wheel using a Hall Effectsensor to sense the passing of a small signal magnet mounted on thewheel at a known angle from the compressor 32. It then determines thespeed and position of the compressor 32 and the time of its nexttransit.

The embodiments described above involve one compressor cycle of oneintake stroke and one output stroke on each passage of the compressor 32by the magnetic element 30. Such embodiments assume that one stroke,such as the intake stroke, occurs during the time period that thecompressor is passing the magnetic element 30. The other stroke occursduring the balance of the wheel revolution. Other embodiments mayreverse the input and output strokes. Further embodiments permit othernumbers of compressor cycles per wheel revolution. For example, twostationary permanent magnets or electromagnets 30 may be positioned suchthat the compressor 32 passes both magnets during each wheel revolution,providing two compressor cycles per wheel revolution. Furthermore, amagnet 30 with two poles 87 that are adequately separated in thedirection of relative compressor motion may effect two compressor cyclesduring one wheel revolution if transit of the fields concentrated abouteach pole causes the same one of the two opposing forces.

Whereas magnetic fields of opposite polarity have the same attractingforce on a non-magnetized ferromagnetic actuator, magnetic fields ofopposite polarity provide opposite attracting and repelling forces on amagnetized actuator. Thus, a magnetized actuator 35 may undergoalternating opposite forces upon passing two opposite magnetic poles 87of a magnetic element 30, that are separated adequately in the directionof relative compressor motion as shown in FIG. 8. Thus a completecompressor cycle may occur without a bias force. Such alternatingpolarity fields can be provided by a permanent magnet or electromagnetwith its poles far enough apart, or by two permanent magnets positionedwith opposite poles facing the compressor as it passes. If the currentin the winding 116 of an electromagnet 30 is reversed each wheelrevolution the polarity of its magnetic field is alternated. Acompressor with a magnetized actuator and no bias force will thenexperience alternating opposite forces on sequential wheel revolutionsand complete one compressor cycle in two wheel revolutions. Embodimentswithout a bias force may use a pressure relief valve to establish andregulate the desired tire inflation pressure.

All of the embodiments described above use a magnetically-drivencompressor. The following embodiments use an electric coil 104 totransit the magnetic field 36 of the magnetic element 30 and relay theinduced electrical energy received by the coil 104 to anelectrically-driven compressor 110. FIG. 9 illustrates an examplearrangement showing a coil 104 connected by wire 98 to anelectrically-driven compressor 110 mounted over a wheel hub 99 andsending the output air through a pneumatic tube 70 to the valve stem 72.As the electrical coil 104 transits a magnetic field 36, a pulse of onepolarity is induced as the coil 104 enters the magnetic field 36 and apulse of opposite polarity is induced as the coil 104 leaves themagnetic field 36, if the field 36 is wider than the coil 104. Further,it is also possible that if the poles are far enough apart, they mayeach drive an opposing force on a magnetized actuator and operatewithout a bias force. Such electrical pulses may directly drive anelectrically-driven compressor 110. Almost any magnetically-drivencompressor configuration may be converted to an electrically-drivencompressor by attaching an electromagnet 38 that produces the type ofmagnetic field needed by the magnetically-driven compressor 32.

FIGS. 10 and 11 illustrate another embodiment using an electromagnet 38for the magnetic element, and an electrical coil 104 that may transitthe magnetic field. The combination of electromagnet 38 and electriccoil 104 form an intermittent split pulse transformer 102 with atwo-piece core. The transformer 102 may comprise two separate pieces,with the electromagnetic winding 116 on the electromagnet 38 serving asa primary winding on its portion of the transformer core, and theelectrical coil 104 serving as a secondary winding and its portion ofthe core. The primary winding of the electromagnet 38 is mounted on astationary element of a wheel assembly. The secondary winding of theelectrical coil 104 is mounted on the wheel 22 where it passes near theprimary winding once each wheel revolution. The split transformer 102 isoperative during the period in which the two core portions are closeenough to provide good magnetic communication. The central controller100 may activate the primary winding only when there is satisfactorymagnetic communication with the secondary winding. The switch 76 may bea pressure activated switch that limits the maximum pressure if a biasforce is not used to regulate the pressure. The electrically-drivencompressor 110 may be located anywhere on the wheel 22, preferably overthe wheel hub 99. As discussed herein, the transformer 102 may be usedin a variety of manners.

For example, the transformer 102 may provide power to other on-wheelcomponents for assisting in maintaining tire pressure, such ascontrollers, sensors, electrical energy storage devices, and/orcompressors. As shown in FIG. 12, the output of the transformer 102 onthe wheel may feed an on-wheel electronic power supply 112 that providespower in the form needed by on-wheel electronic elements and may alsorecharge a storage capacitor or a rechargeable battery 114 to storeelectrical energy for later use. Further, the transformer 102 maytransfer pulse coded data in both directions between the controllers onthe vehicle frame and on the wheel 22. Those familiar with the TPMS mayrecognize FIG. 12 as a combination of a TPMS and pressure maintenancedevice where the transformer 102 may serve the TPMS or compressor 110 orboth. An on-wheel controller 120 may control the compressor 110 based oninformation from in-tire pressure and temperature sensors 124. Apressure activated switch 76, or pressure limit valve 74, or the biasforce may limit the output pressure to the desired tire inflationpressure. The electrically-driven compressor 110 may be located anywhereon the wheel 22, preferably over the wheel hub 99.

FIG. 12 expands on the embodiment in FIG. 11 by adding an on-wheelcontroller 120, an on-wheel power supply 112, a simple driver display128, and a small rechargeable battery 114. The power supply 112, asdescribed above, permits use of any type of electrically-drivencompressor and provides power for any on-wheel electronics. The on-wheelcontroller 120, preferably a microprocessor, may control compressoroperation and the two-way data communication capability provided by theintermittent transformer 102. The on-wheel controller may receivecontrol instructions from the central controller 100. It may send dataregarding at least one of the compressor 110 utilization and output flowrate. The flow rate derived from a sensor in the output port 66 may besent to the central controller 100. The central controller 100 sends analert to the driver display 128 suggesting a possible leak when theutilization or flow rate of any wheel exceeds a predetermined thresholdfor a predetermined period. Similarly, it sends an alert to the driverdisplay 128 when the utilization or flow rate has been zero for apredetermined period, suggesting possible failure of the device 12. Thealerts indicate the wheel involved and nature of the alert. The smallrechargeable battery 114, illustrated in FIGS. 11 and 12, is keptcharged by a charging circuit in the power supply 112, and adds twovaluable features. It provides power storage and smoothing for anyon-wheel electronics and provides emergency power for brief periods ofmaximum speed compressor operation for a tire suspected of having asignificant leak. In normal operation, the low duty cycle of powertransfer through the intermittent transformer 102 limits compressoroperation to that adequate for replacing normal leakage. In anemergency, such as when the driver is notified of a suspected leak, thecompressor is operated at its highest speed on continuous power from thebattery 114 until the battery 114 is completely discharged. This mayallow a driver more time to find a safe stopping place before a leakingtire goes flat. A TPMS may benefit from the two-way communicationsbetween the wheel 22 and the vehicle and the rechargeable battery 114 topower the on-wheel electronics.

Addition of temperature and pressure sensors 124 to tires in the FIG. 12embodiment allows adding the primary function of a TPMS, warning thedriver when any tire 14 is significantly under-inflated. However, anyvalue of such TPMS-like warnings is greatly reduced since significantunder-inflation is unlikely to occur in this embodiment unless there isa significant leak in a tire or a device failure, which may be sensedand trigger alerts to the driver without in-tire sensors.

FIG. 13 illustrates an embodiment with the same features as in theembodiment in FIG. 12. However, the magnetically-driven compressor 32and electrical coil 104 transit the magnetic field separately. Thus, amagnetically-driven compressor 32 is used instead of anelectrically-driven compressor 110. The coil 104 and power supply 112serves only the electronics and rechargeable battery 114 and not themagnetically-driven compressor 32.

As will be recognized by one of skill in the art, the aforementionedembodiments may be variously modified. For example, multiple pulses maybe applied during one transit of a compressor or a coil past anelectromagnetic; the magnetic element may be mounted on any stationarymember (non-rotating part) of the wheel assembly from which it can bepositioned close enough to the rotating compressor or coil; thecompressor or electrical coil may be located anywhere that rotates withthe wheel and passes near the magnetic element; any of theimplementations described above can use multiple magnetic elementsand/or multiple compressors or electrical coils on one wheel assembly;the devices may be used on wheels of any type of vehicle with inflatabletires; different types and configurations of magnets, compressors andelectrical coils may be used; various combinations of magnets,compressors bias force means, pressure limit means, input and outputmeans, check valves, element mounting means and configurations may beused.

Most of the above combinations of techniques are obviously still validwhen some features are omitted. The means of driving a compressor is oneof the important features of the present invention, not necessarily thenature of the compressor (therefore, piston-cylinder compressors,bellows compressors, diaphragm compressors, motor-driven compressors,solenoid compressors, and other types of compressors may also besubstituted as viable compressors in embodiments of the presentinvention).

The above description is given by way of example, and not limitation.Given the above disclosure, one skilled in the art could devisevariations that are within the scope and spirit of the inventiondisclosed herein, including various ways of utilizing or modifyingembodiments of the present invention. Further, the various features ofthe embodiments disclosed herein can be used alone, or in varyingcombinations with each other and are not intended to be limited to thespecific combination described herein. Thus, the scope of the claims isnot to be limited by the illustrated embodiments. Other modificationsmay be variously implemented utilizing the teachings found herein.

1. A device for maintaining a desired inflation pressure of an interiorof a tire mounted on a wheel of a vehicle, the wheel being rotatablyconnected to a stationary member of a vehicle wheel assembly anddefining an axis of rotation, the device comprising: at least onemagnetic element being mounted on the stationary member at a radialdistance from the axis of rotation, the magnetic element producing amagnetic field wherein the magnetic element produces at least one of twoopposing forces; a magnetically driven air compressor being mounted onthe wheel and being radially disposed from the axis of rotation relativeto the magnetic element to transit the magnetic field during eachrevolution of the wheel, the compressor being in fluid communicationwith the atmosphere and the interior of the tire, the compressor beingoperative to intake air from the atmosphere and to output compressed airto the interior of the tire in response to transiting the magnetic fieldwherein the compressor includes a flexible compression chamber defininga variable chamber volume; and means for regulating output pressure ofthe compressor to the desired inflation pressure without off-wheel aid;an actuator being operative to increase and decrease the chamber volume,the actuator being operative to effect an intake stroke to increasechamber volume and thereby intake air from the environment through anintake check valve, the actuator further being operative to effect anoutput stroke to decrease chamber volume and thereby expel air throughan output check valve; and means for applying first and second opposingforces alternately to the actuator, one of the first and second opposingforces increasing the volume of the flexible chamber and the other ofthe first and second opposing forces decreasing the volume of theflexible chamber, at least one of the first and second opposing forcesbeing produced upon transit of the compressor through the magneticfield.
 2. The device of claim 1 wherein the flexible compression chamberis a bellows configuration having two opposing ends and flexible sidewalls, the first opposing end being in communication with the intakecheck valve and the second opposing end being in communication with theoutput check valve, the actuator being operative to increase the chambervolume to intake air into the compression chamber through the intakevalve upon the actuator moving to an intake position during the intakestroke, the actuator being further operative to decrease the chambervolume and expel compressed air from the compression chamber through theoutput valve upon moving to an output position during the output stroke,one of the input stroke and output stroke being performed in response tothe compressor transiting the magnetic field.
 3. The device of claim 1wherein the flexible compression chamber is bounded on one side by aflexible diaphragm, and being operative to increase the chamber volumeto intake air into the compression chamber through the intake valve uponthe actuator moving to an intake position during the intake stroke, theactuator further being operative to decrease the chamber volume andexpel compressed air from the compression chamber through the outputvalve upon moving to an output position during the output stroke, one ofthe input stroke and output stroke being performed in response to thecompressor transiting the magnetic field.
 4. The device of claim 3,wherein the flexible diaphragm further comprises ferromagnetic particlesembedded in the flexible diaphragm wherein the flexible diaphragm servesas the actuator.
 5. The device of claim 1 including two stationarymagnetic elements and wherein the compressor transits through twomagnetic fields produced by the magnetic elements during one revolutionof the wheel, both magnetic fields exerting the first opposing forceupon the actuator to perform one of the input and output strokes, thesecond opposing force being exerted upon the actuator to perform theother of the input and output strokes as the compressor movesintermediate the magnetic elements, the alternate exertion of the firstand second opposing forces causing the chamber volume to increase anddecrease twice during one wheel revolution.
 6. The device of claim 1,wherein the compressor transits magnetic fields of opposite polaritycausing sequential opposing magnetic forces on a magnetized actuator. 7.The device of claim 6, wherein the magnetic fields of opposite polarityoriginate from opposite poles of one or more permanent magnets.
 8. Thedevice of claim 6, wherein the magnetic fields of opposite polarity arecreated by reversing the direction of current through one or moreelectromagnetic elements after the compressor transits at least one ofthe magnetic fields.
 9. The device of claim 1 wherein a plurality ofmagnetic elements are configured to produce successive magnetic fieldsof opposite polarity through which the compressor transits during onerevolution of the wheel, the input and output strokes being effected bythe magnetized actuator in response to the magnetic fields of opposingpolarity.
 10. The device of claim 1 wherein the second opposing force isa continuous bias force being produced by one or more permanent magnets,the second opposing force being configured to be overcome by the firstopposing force produced when the compressor transits the magnetic fieldof the stationary magnetic element, the second opposing force causingthe actuator to effect one of the input and output strokes aftertransiting the magnetic field.
 11. The device of claim 1 wherein thesecond opposing force is a bias force being produced by a spring biasingmember, the second opposing force being configured to be overcome by thefirst opposing force produced when the compressor transits the magneticfield of the stationary magnetic element, the second opposing forcecausing the actuator to effect one of the input and output strokes aftertransiting the magnetic field.
 12. The device of claim 1 wherein thesecond opposing force is the centrifugal force being continuouslyexerted upon the actuator due to rotation of the compressor about theaxis of rotation of the wheel, the second opposing force causing theactuator to effect one of the input and output strokes after transitingthe magnetic field.
 13. The device of claim 1 wherein the secondopposing force is configured to establish and regulate the desiredinflation pressure of the tire.
 14. The device of claim 1 wherein thecompressor further includes an output port and a pressure limit valve,the output port being in fluid communication with the flexiblecompression chamber with the output valve being open, the pressure limitvalve being in fluid communication with one of the output port and theflexible compression chamber, the pressure limit valve being operativeto reduce the output pressure of air within the respective one of theoutput port and the flexible compression chamber to the desired tireinflation pressure by releasing air from the respective one of theoutput port and the flexible compression chamber to one of theatmosphere and intake plenum when the output pressure exceeds thedesired tire inflation pressure.
 15. The device of claim 1 wherein themeans for regulating the output pressure of the compressor permitsmanual adjustment of the desired tire inflation pressure.
 16. The deviceof claim 1 wherein the means for regulating the output pressure of thecompressor varies the desired inflation pressure as a function oftemperature of the air in the tire.
 17. The device of claim 16 whereinthe desired inflation pressure changes with the temperature of air inthe tire tending to maintain a constant mass of air in the tire.
 18. Thedevice of claim 1 wherein the compressor includes an intake port and acentrifugal valve, the intake port being in fluid communication with theatmosphere, the centrifugal valve being operative to shut off all airand fluid entry into the compressor via the intake port while the wheelis rotating below a predetermined speed.
 19. The device of claim 1wherein the magnetic element is an electromagnet controlled by a centralcontroller on the vehicle frame that receives electrical current from avehicle battery and sends the current through the electromagnet windingto produce the magnetic field, the central controller being furtheroperative to produce the current only during periods when the compressoris transiting the magnetic field.
 20. A device for maintaining a desiredinflation pressure within a tire mounted on the wheel of a vehicle, thewheel being rotatably connected to a stationary member of a vehiclewheel assembly and defining an axis of rotation, the device comprising:at least one magnetic element being mounted on the stationary member ata radial distance from the axis of rotation, the magnetic elementproducing a magnetic field; an electrical coil mounted on the wheel andbeing radially disposed from the axis of rotation relative to themagnetic element to pass through the magnetic field during a revolutionof the wheel, the coil being operative to induce electrical voltagevariations in response to the transit of the magnetic field and tooutput the electrical voltage variations for powering the device; an aircompressor mounted on the wheel being powered by electrical voltagevariations induced in the coil by transiting the magnetic field, the aircompressor in electrical communication with the coil and in fluidcommunication with the atmosphere and an interior of the tire, thecompressor further operative to output compressed air into the tire;electronic elements that alert a vehicle driver to tire pressureconditions and means for regulating the output pressure of the aircompressor to the desired tire inflation pressure without off-wheel aid.21. The device of claim 20, further comprising an adjustable pressurelimit switch in electrical communication with the electrical coil andthe air compressor, the pressure limit switch being activated by tirepressure and operative to regulate the desired inflation pressure of thetire.
 22. The device of claim 20, wherein the means of regulating theoutput pressure of the compressor varies the desired inflation pressureas a function of the temperature of air in the tire.
 23. The device ofclaim 21, wherein the desired inflation pressure is varied as a functionof the temperature of the air in the tire so as to maintain a constantmass of air in the tire.
 24. The device of claim 20, wherein themagnetic element is an electromagnet operative to generate a current toproduce the magnetic field only when the electrical coil is transitingthe magnetic field during the rotation of the wheel.
 25. The device ofclaim 20, further comprising an electrical power supply that receivesoutput from the electric coil and converts the output from theelectrical coil into electrical power usable by at least one of the aircompressor and the on-wheel electronics.
 26. The device of claim 25,further comprising an on-wheel rechargeable electrical storage deviceconfigured to store electrical power for at least one of the aircompressor and the on-wheel electronics.
 27. The device of claim 20,wherein the magnetic element is an electromagnet that serves as aprimary winding of an intermittent split transformer with the electricalcoil forming a secondary winding of the split transformer, the splittransformer being operative while the primary and secondary windings arein magnetic communication, the split transformer being operative toperform one of transferring electrical power from the vehicle to thewheel and providing two-way pulse data communication between the vehicleand the wheel.
 28. The device of claim 27 further comprising: anon-wheel power supply operative to receive the voltage output of thesecondary winding and to convert the voltage output to an electricalform needed to satisfy electrical power needs for at least one of thecompressor and the on-wheel electronics; a driver display beingoperative to inform a driver of a suspected leak or failure of a givenwheel; a central controller mounted on the vehicle and operative to sendand receive pulse coded data to and from the primary winding while thetransformer is operative; the central controller being in electricalcommunication with a vehicle battery, the primary winding, and thedriver display; the central controller being operative to determine whencompressor operation is high enough to suspect a leak or low enough tosuspect a failure, the central controller being operative to send datato the driver display being representative of the compressor operation;an on-wheel controller operative to send and receive pulse coded data toand from the secondary winding while the transformer is operative; theon-wheel controller being in electrical communication with the secondarywinding, the on-wheel power supply, and the compressor; the on-wheelcontroller being operative to sense compressor operation and to maintainthe desired tire pressure, the on-wheel controller further beingoperative to send data corresponding to the compressor operation to thecentral controller and means for communicating the pulse coded databetween the vehicle and the wheel assembly.
 29. The device of claim 28,further comprising a rechargeable electrical storage device inelectrical communication with the on-wheel power supply, therechargeable electrical storage device operative to store electricalpower and operate as a filter and D.C. source for providing reservepower to operate the compressor at a high speed when a failure issuspected.
 30. The device of claim 28, further comprising tire sensorsbeing operative to sense tire pressure and tire temperature, the sensorsbeing disposed on each wheel and being in electrical communication withthe on-wheel power supply and the on-wheel controller;